This invention relates to a method of evaluating an object in which an input image is processed using fuzzy logic, and to an inspection apparatus in which this evaluation method is applied to, e.g., inspection of circuit board mounting.
In recent years there has been increasing demand for electronic devices which are smaller in size and weight and provided with a multiplicity of functions. Surface mounting techniques are being developed in order to satisfy this demand.
However, it has not been long since the birth of surface mounting techniques, and since precedence has been given to the miniaturization of parts, it cannot truly be said that these techniques have firmly taken root in production processes. Much progress still needs to be made in these techniques. In particular, there is a special demand for automation of a process for inspecting the external appearance of objects.
Items which need to be inspected by an automatic apparatus for inspecting external appearance are as follows, by way of example:
(1) the absence or presence of parts, and whether parts are mounted in the proper attitude; PA1 (2) whether the mounted state of a part is proper or faulty; PA1 (3) whether or not a mounted part is the wrong part; and PA1 (4) whether the soldered state of a part is proper or faulty.
It is hoped that inspection of all of these items which presently are inspected visually will be performed by an automatic inspection of external appearance.
With regard to items (1) through (3), image processing is adequate and a variety of inspection apparatus which rely upon image processing are available on the market. In connection with the inspection of soldered condition in item (4), quantitative evaluation is difficult. For this reason, though various methods have been proposed and given consideration, reliable methods have yet to be developed and the state of the art is such that almost all of these methods rely upon visual inspection.
Accordingly, the inventors have considered applying image processing technology to inspection instead of relying upon visual inspection. Clustering processing is known as one image processing technique capable of being applied to inspection of a mounted state in order to evaluate the mounted state. Clustering entails evaluating certain characterizing quantities based upon reference data. More specifically, clustering involves matching a reference pattern and an input pattern and categorizing an input pattern having a high degree of similarity in a class the same as that of the predetermined reference pattern.
However, in a case where the aforementioned conventional clustering is used in evaluation of an input image in image processing (e.g., evaluation of the mounted state of a part on a printed circuit board), a recognition error can arise if a characterizing quantity is evaluated unconditionally. There is the danger that this will have a deleterious influence upon image processing.
In addition, when the characterizing features of an image are evaluated, it stands to reason that there will be characterizing quantities which do not lend themselves to evaluation by clustering processing.